Conventionally, various kinds of rotary electrical machines each including an annular stator around a round columnar rotor have been developed. The rotor includes a rotor core in which a plurality of core sheets made up of magnetic steel plates are laminated, a magnet hole formed in the rotor core, and a magnet embedded in the magnet hole.
In order to reduce noise generated in rotating the rotor, Japanese Patent Application Laid-Open No. 2006-254598 described below discloses a rotor in which the magnet hole is deviated (skewed) in a circumferential direction of the rotor (that is to say, a circumferential direction with respect to a rotational axis) as the magnet hole gets closer from one end in a direction parallel to a rotational axis of the rotor (referred to as “the axial direction” hereinafter) toward the other end.
The rotor in which the magnet hole is skewed has a magnetic pole center moving in the circumferential direction from the one end in the axial direction of the rotor toward the other end. Accordingly, variation in reluctance and a gradual change in magnetomotive force caused by a rotational position of the rotor are reduced. The above configuration reduces a cogging torque and a torque ripple, and the noise is reduced. There are cases where the skew is performed on each one core sheet and the skew is performed in stages by the plurality of core sheets (step skew).
In the rotor to which the step skew is applied, a non-magnetic body is disposed on a boundary at which the magnet hole is skewed to prevent leakage flux. When a bond magnet is injection-molded in the magnet hole, the bond magnet is preferably formed with a single injection molding. It is therefore necessary to also provide the non-magnetic body described above with the magnet hole. The bond magnet is formed in each magnet hole of the core sheet and the non-magnetic body.
However, a portion of the non-magnetic body is not influenced by a magnetic field, and a magnetic pole cannot be formed on an outer periphery thereof. Thus, the bond magnet formed in the magnet hole in the non-magnetic body cannot contribute to the torque of the rotor.